1. Field of the Invention
The present invention relates to a synchronization establishment method which is suitable to be used for a communication system conforming to IEEE 1588 Ver. 2 which is a protocol for performing synchronization between apparatuses via a local network such as Ethernet (registered trademark).
2. Description of the Related Art
The above-described IEEE 1588 Ver. 2 defines that, when synchronization is established between a base station (hereinafter, referred to as a “master station”) serving as a master and a base station (hereinafter, referred to as a “slave station”) serving as a slave, the master station transmits a message such as “Sync” every second.
IEEE 1588 Ver. 2 also defines an option for establishing synchronization in a short period of time. Sync when this option is used is temporarily referred to as Sync2.
The above-described technique, that is, a technique for establishing synchronization by using a local network is known. For example, Japanese Patent Unexamined Publication (Translation of PCT application) No. 2003-509973 discloses a synchronization method for a plurality of base stations in a mobile communication network. This synchronization method is a synchronization method for a plurality of base stations in a mobile communication network, in which time information is transmitted to the plurality of base stations via a local network (LAN), a clock generator of each base station which receives the time information is adjusted on the basis of a reception time point and time information content of the time information, and transmission of a function sequence related to a wireless time frame to each base station is controlled on the basis of a signal of the clock generator.
However, in IEEE 1588 Ver. 2, in a case where the option for establishing synchronization in a short period of time is used, Delay_Req is also returned in a short cycle in relation to Sync2, and thus there is a problem in that, as the number of slave stations increases, the load on the master station increases, and synchronization cannot be established in a case where the resource capability of the master station is exceeded.